The Golden Sayings of Epictetus, 107

We must approach this matter in a different way; it is great and mystical: it is no common thing; nor given to every man.

Wisdom alone, it may be, will not suffice for the care of youth: a man needs also a certain measure of readiness--an aptitude for the office; aye, and certain bodily qualities; and above all, to be counselled of God Himself to undertake this post; even as He counselled Socrates to fill the post of one who confutes error, assigning to Diogenes the royal office of high reproof, and to Zeno that of positive instruction. Whereas you would fain set up for a physician provided with nothing but drugs! Where and how they should be applied you neither know nor care.